The long term goal of this project is to understand the biomechanical function of the cruciate ligaments through an extensive and detailed study of the forces developed in these important structures. Through a series of controlled loading tests on fresh cadaveric knee specimens, forces in the cruciate ligaments and cruciate graft substitutes will be measured. Knowledge of cruciate ligament forces (and the types of knee loadings which produce them) is important for identifying and understanding mechanisms of injury, and for formulating recommendations of post-operative activities, protective measures, and rehabilitation exercises which will limit forces generated in a ligament which has undergone repair, augmentation, or substitution. A unique experimental technique will be used to directly measure resultant force in the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) using cadaver specimens. This technique involves mechanical isolation of a bone plug containing the tibial attachment of the ACL and femoral attachment of the PCL, and fixation of each bone plug onto specially designed miniature load cells which measure resultant forces in the ligaments as external loads are applied to the tibia. Attachment of an isometer wire to the undersurface of the isolated bone plug permits displacement measurements of the bone caps relative to the femur as the knee is flexed, giving information related to isometry of the native cruciate ligaments. Five Specific Aims will be investigated. Aim 1: The effects of femoral tunnel hole location upon AP limits of knee motion and forces developed in an ACL patellar tendon graft substitute will be studied during straight tibial loading experiments. In addition, length changes of the distal ends of ACL wire substitutes and ACL graft substitutes (relative to the tibia) will be measured during knee flexion for three femoral tunnel hole locations. Aim 2: The effects of notchplasty size upon graft pretension required to restore normal AP limits of tibial motion, and upon forces developed in an ACL patellar tendon graft substitute will be measured during straight tibial loading experiments. Aim 3: The relationships between graft pretension, AP limits of motion, and force developed in a PCL bone-patellar tendon-bone graft substitute will be studied. Displacements of the femoral bone cap attached to the native PCL (relative to the tibia), proximal end of a PCL wire substitute, and proximal end of a PCL graft substitute will be measured during knee flexion. Aim 4: Forces generated in both cruciate ligaments under combined tibial loadings (two straight loading modes applied simultaneously) will be studied. Aim 5: Relationships between the outputs of force and strain sensors implanted in the cruciate ligaments and total ligament force (as recorded by the cruciate load cells) will be determined during straight loading experiments.